1. Field of the Invention
This invention relates in general to a feeder of an organometallic compound which is solid at room temperature and a method of manufacturing it, and more particularly to a feeder which can supply the organometallic compound which is solid at room temperature without waste and at a stable concentration over an extended period of time, and useful as a material for epitaxial growth by means of the MOCVD (Metalorganic Chemical Vapor Deposition) method for manufacturing compound semiconductors, as well as a method of manufacturing this feeder.
2. The Prior Art
In recent years, the compound semiconductors of the III-V group and II-VI group in the periodic table have been employed in a wide variety of technical fields including semiconductor light emitting elements and microwave transistors. Further, these compound semiconductors have been used in integrated circuits for high speed computers, integrated circuits for optoelectronics and such due to their superior characteristics.
The compound semiconductors used in these diversified applications are manufactured with the MOCVD method for growing the crystals using organometallic compounds. The MOCVD method is one of the crystal growth methods often used to form an epitaxial thin film of a compound or mixed crystal semiconductor. In the MOCVD method, an organometallic compound such as trimethyl indium, trimethel aluminum or trimethyl gallium is used, and the crystal growth of the thin film is carried out by utilizing the thermal decomposition of the source material.
These organometallic compounds used in the MOCVD method a re usually filled in a hermetic container which has two outputs for feeding and discharging gas. A carrier gas such as hydrogen is fed into the container through the feeding output and the carrier gas saturated with vapor of the organometallic compound is obtained from the discharging output.
In general, the organometallic compound which is solid at room temperature is filled in the container where the organometallic compound is adhered to the inner wall of the container as a granular form. However, it is difficult to supply the solid organometallic compound at a constant concentration in the carrier gas. In more detail, since it is difficult to maintain a homogeneous contact between the carrier gas and the solid organometallic compound, the contact area changes. As a result, it is diffficult to feed the solid organometallic compound at a constant concentration.
The electrical and optical characteristics of an intermetallic compound which is formed by epitaxially growing an organometallic compound are significantly affected when the composition ratio of the solid organometallic compound changes during the growth. Therefore, in order to obtain high performance semiconductor elements, it is necessary to supply the organometallic compound steadily at a constant concentration. Also, feeding of the solid organometallic compound is required to be achieved by using only a vaporization container without a complex apparatus.
Particularly, when a solid organometallic compound such as trimethyl indium is fed by the same container as one used for liquid organometallic compounds by the bubbling method in which the carrier gas is bubbled, the feeding rate of solid organometallic compounds changes, depending on the amount of the organometallic compound in the container. As a result, it is difficult to feed the organometallic compound under constant conditions until it runs out.
There have been proposed several methods to solve these problems until now. One of which has proposed that an organometallic compounds is supported by solid support filled in a container (Japanese examined patent publication Tokko Hei 6-20051), and another has proposed that an organometallic compounds is coated on a solid support filled in a container (Japanese unexamined patent publication Tokkai Hei 1-265511).
However, in the first mentioned method, stability in the concentration of the organometallic compounds is not sufficiently improved and the concentration may gradually decrease. In the second mentioned method, it is also difficult to feed the organometallic compounds for a long duration at a constant concentration. Further, the concentration of the organometallic compounds in the carrier gas may not effeciently increase even if the amount of the organometallic compounds coated on the solid support increases unless the amount of the support as well as the organometallic compounds increases. Therefore, a large container is required to contain more solid support, which is not an economical way.